In particular, yet not restrictive manner, the invention concerns a mechanical locking system for rectangular building panels with long and short edges. It should be emphasized that long and short edges are only used to simplify the description. The panels could also be square, they could have more than 4 edges and the adjacent edges could have angles other than 90 degrees. However, the invention is as well applicable to building panels in general. More particularly the invention relates mainly to the type of mechanically locking systems, which allow that angling of long edges and vertical movement of short edges could lock all four edges of a panel to other panels.
A floor panel of this type is presented in WO2006/043893, (FIG. 1a) which discloses a floor panel with a locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a flexible tongue (30) cooperating with a tongue groove (20), for locking in a vertical direction. The flexible tongue bends in the horizontal plane and snaps into the tongue groove during connection of the floor panels and makes it possible to install the panels by vertical snap folding or solely by vertical movement. Similar floor panels are further described in WO2003/016654, which discloses locking system comprising a tongue with a flexible tab. The tongue is extending and bending essentially in a vertical direction and the tip of the tab cooperates with a tongue groove for vertical locking.
Vertical locking and vertical folding of this type creates a separation pressure at the short edges when the flexible tongue or flexible parts of the tongue are displaced horizontally in a double action during the angling of the long edges. Parts of the tongue are displaced inwardly during the initial part of the locking and they are thereafter displaced towards the initial position during the final part of the locking action. The inventor has analyzed several types of floor panels and discovered that there is a considerable risk that the short edges could be pushed away from each other during installation and that a gap could occur between the edge portions of the short edges. Such a gap could prevent further installation and the floor panels will not be possible to connect. It could also cause serious damage to the locking system at the short edges. Pushing the floorboards sideways towards the short edges during installation could prevent the gap. Such an installation method is however complicated and difficult to use since three actions have to be combined and used simultaneously in connection with angling down of the long edges.
It is also known, as shown in FIG. 1b that two adjacent short edges in a first row could be locked with a displaceable tongue (30), which is displaced and, for example, bended by a side push at one edge section (32) when the adjacent short edges have been folded down and positioned in the same plane. Such an installation is described in DE 1020060376114B3 and a pre published PCT application made by Välinge innovation AB. This vertical push folding, which generally is activated by a pressure from a long side of a third panel in a second row, displaces the separate tongue along the short edge joint but also perpendicular to the joint direction such that a part of the tongue is displaced into a groove of the adjacent short edge. This displacement perpendicular to the joint direction avoids the separation forces during the vertical folding but creates a separation force when the panels are laying flat on the sub floor and when the tongue is pressed into the tongue groove of the adjacent panel. This side push pressure parallel to the joint must be converted to a pressure force perpendicular to the edge and this is a disadvantage since a considerable part of the pressure will be lost and cannot be used to create a strong locking force that brings the edges in the same plane in case that they are warped. Most vertical push folding systems, especially such systems that comprise a flexible tongue that bends in the length direction of the joint, are difficult to lock when the first and the last rows are installed. They are not suitable to lock wide panels. Some of these problems could be avoided with a wedge shaped tongue. Such wedge shape tongues consist generally of two parts or they are connected to grooves, which are not parallel with the edge. This leads to the fact that expensive materials or complicated production methods must be used.
JP 3110258 (Matsushita) discloses a raised floor for office buildings, e.g. in a computer room, with a high requirement of access to cables or pipes under the front face. The raised floor comprises units, which can be locked, after they have been positioned on the sub-floor, with a displaceable magnetic tongue, which is displaced from one groove in one edge of a unit to another groove in an adjacent unit with a magnetic force. Matsushita teaches that such floorings cannot be provided with tongues.